1) Field of the Invention
The present invention relates to variable sweep aircraft and, more particularly, to a pivoting aircraft wing capable of varying the sweep angle of an aircraft, as well as an associated system and method.
2) Description of Related Art
It is well known that wing design plays an instrumental role in optimizing lift and drag during flight in response to various conditions. Wing design becomes especially important depending on whether the wing is subjected to subsonic, transonic, or supersonic speeds. Decreasing drag involves balancing several different parameters, including, for example, speed, altitude, angle of attack, wing dimensions, and the profile of the airfoil.
Wings having a high span are preferred for takeoff and landing where drag is substantially lower than wings having a low span. Because the aspect ratio is defined as the ratio of the wing span to the average chord length, longer and narrower wings will have better lift than shorter and wider wings. However, swept wings are preferred over high aspect ratio unswept wings at transonic and supersonic speeds because drag is significantly reduced. Even though swept wings can also maintain the required lift at these higher speeds, swept wings do not perform well at subsonic speeds. Therefore, swept wing aircraft are generally required to have lower sweep angles than would typically be required for transonic and supersonic speeds in order to make takeoff and landing feasible.
Therefore, variable sweep aircraft wings have been developed that are able to balance the tradeoffs of using either a high aspect ratio, unswept wing, or a lower aspect ratio, swept wing. Aircraft with variable sweep wings can modify the wing configuration from a high span during takeoff, subsonic cruise, or landing, to an increased sweep during supersonic speeds. Advantageously, aircraft with variable sweep wings are able to decrease weight due to an increase in fuel efficiency and may require smaller engines to accelerate the aircraft to supersonic speed, in addition to being capable of operating over a wide range of speeds, decreasing noise due to decreased drag, and shortening takeoff and landing field lengths.
For example, U.S. Pat. No. 4,212,441 to Ascani, Jr. et al (“Ascani”) discloses a wing pivot assembly for a variable sweep aircraft. Ascani discloses a pivot assembly located at the end of each wing adjacent to the fuselage. The pivot assembly includes a pivot pin that utilizes a “pin within a pin” design, where either pin can carry the load limit. A pair of outboard lugs, i.e., plates, located between the wing and the pivot pin acts to carry the wing bending moment loads into the pin, while a second pair of inboard lugs located between the pivot pin and a carry-through structure carry the wing bending moment loads into the carry-through structure. In addition, two bearing assemblies connecting to the outboard lugs facilitate rotating of the pivot pin and also transmit wing bending moment loads from the outboard lugs into the pivot pin. Ascani also employs a shear bearing and the “truss concept,” which includes canting the inboard and outboard lugs at an angle, to counter axial shear loading.
However, previous variable sweep aircraft, such as that discussed above, have inherent disadvantages, namely increased weight, which counteracts any advantages associated with varying the sweep of the wings. In addition, the pivot pin design and excess weight offer a poor mechanical advantage and offset load paths. The support structure surrounding the pivot pin may extend quite far out into the outboard wing box in order to direct the loads away from a wide wing box geometry and toward the pin in a way that does not exceed material strength limits. The same is true of the inboard bearing support structure. Therefore, in addition to a potentially large and heavy pivot pin, the supporting structures add even more weight in transferring loading from the wings to the pivot pin and further inboard to a carry-through structure. Furthermore, the thickness of the wing is required to be at least as thick as the pivot pin, and even wider to accommodate the surrounding support structures, which also increases weight and drag, especially for supersonic aircraft.
It would therefore be advantageous to provide a lighter weight pivoting aircraft wing that can vary the wing sweep angle of an aircraft. In addition, it would be advantageous to provide a pivoting aircraft wing that can vary the sweep angle without sacrificing lift and drag. Finally, it would be advantageous to provide a pivoting aircraft wing that enables an aircraft to travel at supersonic speeds without increasing drag.